Rheological characteristics of binary composite gels of wheat flour and high amylose corn starch.

The effect of addition of high amylose corn starch (Hylon VII or H) to wheat flour (WF) on the mechanical properties of the resulting binary composite gels (BCG) under small and large deformations was evaluated. To this end, the composite gels at different ratios of WF/H including 95:5, 90:10, and 85:15 were tested under a linear viscoelastic regime (LVE) in oscillatory angular frequency and a texture profile analysis in compression mode. However, the gel firmness was increased by Hylon VII addition, but the springiness was reduced. Since the adhesiveness and cohesiveness were not significantly different, no dilution effect was observed for the samples. Furthermore, the dominance of G' than G″ over the range of LVE and high fracture stress at high level of Hylon VII confirmed the high gel strength which can be attributed to the retrogradation of amylose and reduction of amylopectin from WF. The less frequency dependency of BCG revealed the solid-like response and strong gels structures with more elastic network. High value of α revealed a lower number of interactions within the gel network structures. Consequently, due to the high gel strength of BCG of WF/H, it can be exploited at high thermal operations such as retort processing as well as it can be utilized for dysphagia therapy due to the special textural parameters. PRACTICAL APPLICATIONS: Small and large deformation properties can provide profound insights toward the gel structure. The former gets knowledge about dynamic rheology and the latter gives the textural properties of the gel matrices. Since, achieving the desired texture of foods has a chief impact on the target consumers, and chewing and swallowing disorders such as dysphagia are common problems in older people, more effort is needed to modify the texture of food with a soft structure. On the contrary, supplying a more gel strength network, which can withstand at high thermal processing and not collapse, is so vital. Therefore, the current work was accomplished to provide some knowledge about the binary composite gel of WF and Hylon VII starch such as the gel strength, fracture stress, fracture strain and material stiffness which enables us to evaluate the nature of starch gels for further applications such as drug delivery systems, elderly diet and further processes.

Effects of high amylose corn starch and microbial transglutaminase on the textural and microstructural properties of wheat flour composite gels at high temperatures.

Textural and microstructural properties of composite gels (CGs), along with wheat flour and high amylose corn starch (Hylon VII) mixed with microbial transglutaminase (MTGase) at different levels and temperatures were investigated. The results showed by increasing Hylon starch content, the firmness increased and adhesiveness decreased. Indeed, high level of amylose and cross-linking formed by MTGase enhanced the gel elasticity and reduced adhesiveness. Moreover, MTGase had more effect on the firmness and provided more cross-linked intermolecular gel structures at high temperatures. By adding MTGase to the CG, the lowest peak viscosity and final viscosity were found for 15% of Hylon starch. As the more Hylon content in the CG, the more water solubility index was particularly obtained at high temperature. Scanning electron microscopy (SEM) results showed that MTGase and Hylon starch addition enhanced the structure. The differences in SEM of CG were reflected the pasting properties of the gels. Consequently, MTGase treated gels can withstand high temperature as well as maintain the overall structure of the samples gels. Therefore, the increment of Hylon to the CG gels supplied tighter, stronger, and denser protein network which were formed by MTGase cross-linking within the network of starch and proteins. PRACTICAL APPLICATIONS: Although, transglutaminase was practically used in the production of noodles and pasta in Japan, but there is little academic and industrial knowledge concerning its utilization in the pasta or noodles. Moreover, long shelf-life noodle/pasta products have become popular in the Japanese market and in the emergency conditions like as floods or earthquake, but they can be stored for at least 5 months by applying heat treatment at 95C. Here, high amylose corn starch as a resistant starch, wheat flour, and microbial transglutaminase (MTGase) were selected as the main components in the composite gel (CG) systems to elucidate the effects of MTGase and Hylon on the texture, microstructure, and pasting behavior of CGs at high temperatures to produce long-life noodle/pasta products (about 2 years) through retort processing.